No description available.

published_or_final_version / Obstetrics and Gynaecology / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 182-211).

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

No description available.

Thesis (Ph.D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 182-211) Also available in print.

No description available.

Cited2 is a member of the Cited gene family, which has no homology to any other genes. It encodes a transcriptional co-factor that is expressed during early heart formation (cardiogenesis). Embryos lacking Cited2 display a range of cardiac defects including bilaterally identical atria, aortic arch abnormalities, rotation of the aorta and pulmonary artery, and malseptation of the cardiac chambers. The latter results in communication between the aorta and pulmonary artery, the aorta and both ventricles, and the atria and ventricles (with themselves and each other). Cardiogenesis is complex, and requires many different cell types and processes to occur correctly. Some of these cells and processes are external to the primary heart. For example, once the initial muscle cells of the heart form a tube, cells from other regions such as the secondary heart field (adjacent mesoderm) and cardiac neural crest (ectoderm) migrate into this tube, and are required for the formation of additional muscle cells and septa. Furthermore, cardiogenesis also requires correct left-right patterning of the embryo to be established prior to heart formation. To understand the developmental origins of the cardiac defects observed in Cited2-null embryos, the expression pattern of Cited2 and the anatomy of Cited2-null embryo hearts were studied. Subsequently, the expression of genes required for left-right patterning were studied in both Cited2-null and Cited2 conditionally-deleted embryos. This demonstrated that Cited2 may be required in many, possibly all, of the processes required for cardiogenesis. Next this study focused on the role of Cited2 in patterning the left-right axis of the embryo. Firstly, Cited2 was found to regulate the expression of the master regulator of left-right patterning (Nodal). Secondly, Cited2 was shown to regulate the expression of the left-specific transcription factor Pitx2 independently of Nodal. Thirdly, gene expression and conditional deletions of Cited2 suggested that Cited2 might regulate left-right patterning in the paraxial mesoderm, a tissue which has not previously been shown to regulate the left-right axis in the mouse. Lastly, an argument is made suggesting the possibility that all the cardiac defects found in Cited2-null embryos may directly or indirectly stem from a failure of correct left-right patterning.

A mouse embryo culture medium which would allow for in vitro development from 1-cell stage to blastocyst stage could offer many benefits for human research. Previous researchfrom our lab has demonstrated a mouse embryo culture medium named CZB seems to allow for in vivo-like conditions for development. Compared to other commonly used mouse embryo culture media, CZB medium promotes a higher frequency of 1 cell mouse embryos developing to blastocyst stage (Chatot et 1989). A key difference between CZB and other mouse embryo culture media is that CZB contains the amino acid glutamine metabolism is glutamate dehydrogenase (GDH). In order to determine if CZB cultured embryos follow in vivo-like patterns of gene expression for GDH, a quantitative competitive RT-PCR system was designed. A mutant GDH mRNA template was created which lacked a specific restriction enzyme site and was used as a competitive template in quantitative RT-PCR. This system was used to determine the amount of GDH mRNA present in in vivo grown blastocyst stage mouse embryos. It was determined that the amount of GDH mRNA present in in vivo blastocyst stage embryos was 282 fg/embryo. It is believed this system will also allow for quantitation of GDH mRNA in the earlier preimplantation stages of in vivo grown embryos, as well as the preimplantation stages 2-cell to blastocyst of CZB cultured embryos. / Department of Biology

Cited2 is a member of the Cited gene family, which has no homology to any other genes. It encodes a transcriptional co-factor that is expressed during early heart formation (cardiogenesis). Embryos lacking Cited2 display a range of cardiac defects including bilaterally identical atria, aortic arch abnormalities, rotation of the aorta and pulmonary artery, and malseptation of the cardiac chambers. The latter results in communication between the aorta and pulmonary artery, the aorta and both ventricles, and the atria and ventricles (with themselves and each other). Cardiogenesis is complex, and requires many different cell types and processes to occur correctly. Some of these cells and processes are external to the primary heart. For example, once the initial muscle cells of the heart form a tube, cells from other regions such as the secondary heart field (adjacent mesoderm) and cardiac neural crest (ectoderm) migrate into this tube, and are required for the formation of additional muscle cells and septa. Furthermore, cardiogenesis also requires correct left-right patterning of the embryo to be established prior to heart formation. To understand the developmental origins of the cardiac defects observed in Cited2-null embryos, the expression pattern of Cited2 and the anatomy of Cited2-null embryo hearts were studied. Subsequently, the expression of genes required for left-right patterning were studied in both Cited2-null and Cited2 conditionally-deleted embryos. This demonstrated that Cited2 may be required in many, possibly all, of the processes required for cardiogenesis. Next this study focused on the role of Cited2 in patterning the left-right axis of the embryo. Firstly, Cited2 was found to regulate the expression of the master regulator of left-right patterning (Nodal). Secondly, Cited2 was shown to regulate the expression of the left-specific transcription factor Pitx2 independently of Nodal. Thirdly, gene expression and conditional deletions of Cited2 suggested that Cited2 might regulate left-right patterning in the paraxial mesoderm, a tissue which has not previously been shown to regulate the left-right axis in the mouse. Lastly, an argument is made suggesting the possibility that all the cardiac defects found in Cited2-null embryos may directly or indirectly stem from a failure of correct left-right patterning.